CVE ID:	CVE-2020-11739
Description:	An issue was discovered in Xen through 4.13.x, allowing guest OS users to cause a denial of service or possibly gain privileges because of missing memory barriers in read-write unlock paths. The read-write unlock paths don't contain a memory barrier. On Arm, this means a processor is allowed to re-order the memory access with the preceding ones. In other words, the unlock may be seen by another processor before all the memory accesses within the "critical" section. As a consequence, it may be possible to have a writer executing a critical section at the same time as readers or another writer. In other words, many of the assumptions (e.g., a variable cannot be modified after a check) in the critical sections are not safe anymore. The read-write locks are used in hypercalls (such as grant-table ones), so a malicious guest could exploit the race. For instance, there is a small window where Xen can leak memory if XENMAPSPACE_grant_table is used concurrently. A malicious guest may be able to leak memory, or cause a hypervisor crash resulting in a Denial of Service (DoS). Information leak and privilege escalation cannot be excluded.
Test IDs:	None available
Cross References:	Common Vulnerability Exposure (CVE) ID: CVE-2020-11739 Debian Security Information: DSA-4723 (Google Search) https://www.debian.org/security/2020/dsa-4723 https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/5M2XRNCHOGGTJQBZQJ7DCV6ZNAKN3LE2/ https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/YMAW7D2MP6RE4BFI5BZWOBBWGY3VSOFN/ https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/NVTP4OYHCTRU3ONFJOFJQVNDFB25KLLG/ https://security.gentoo.org/glsa/202005-08 https://xenbits.xen.org/xsa/advisory-314.html http://www.openwall.com/lists/oss-security/2020/04/14/2 SuSE Security Announcement: openSUSE-SU-2020:0599 (Google Search) http://lists.opensuse.org/opensuse-security-announce/2020-05/msg00006.html